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S I: i I I /VIITTELHAUSER corporation 7901 Stoneridge Drive,Suite 123 j Pleasanton,California 94588 j Bus: (510) 416-2900 Fax: (510) 416-0957 i� r r October 5, 1992 ' r. 1 Mr. Keith Bullock Unocal Refining and Marketing Division Unocal Corporation 2000 Crow Canyon Place, Suite 400 San Ramon, California 94583 'i 1 SUBJECT: Monitoring and Sampling Report Third Quarter 1992 Unocal Service Station 16348 3788 Tracy Boulevard Tracy, California i Dear Mr. Bullock: ; I , On September 21, 1992 Mittelhauser Corporation ' (Mittelhauser) monitored and sampledjgroundwater monitoring wells MW-2, MW-3 , and MW-4 at Unocal Co'rporation's (Unocal) Service Station #6348 in Tracy, California. ; Earlier sampling events had not detected contamination in wells MW-1, MW-2, and MW-4, while MW- 3 (immediately adjacent to the underground fuel storage tanks) contained petroleum hydrocarbon as gasoline (TPH-G) and components benzene, toluene, ethylbenzene, and xylenes (BTEX) . I j� The September 21 sampling event confirmed the findings of sampling undertaken previously. No TPH-G or BTEX was detected in MW-2 and MW-4 . Hydrocarbons were detected in MW-3 in concentrations similar to those encountered previously. Upgradient j monitoring well MW-1 has been removed from the sampling program, with approval of the San Joaquin County Department of Public Health Services. Well locations are shown in the attached Site Plan (see Figure 1) , l BACKGROUND ,I li + The business at the site I� is a Unocal service station which was in operation from 1972 until March 1992 . i I j i CHICAGO, IL BAKERSFIELD, CA INDIANAPOLIS, IN LAGUNA HILLS, CA i - a